Transmission-measuring system



Feb. 11, 1930. F, H BEST 1,746,239

TRANSMISSION MEASURING SYSTEM Filed Nov 19, 1926 l ATTORNEY Patented Feb..11, 1930 UNITED STATES PATENTl OFFICE FRED H. BEST, OF 7ESTIiIIEdlLDz NEW JERSEY, ASSIGNOR. TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK l l 4 TRANSMISSION -MEASURING SYSTEM'.

` Application filed November 19, 1926. Serial No. 149,511.

This invention relates to transmission measuring systems, and particularly to means for automatically indicating the transmission equivalent of a circuit over which signal-` 5 ing currents are transmitted.

In transmission measuring systems of the prior art, it requires a relatively long period of time for the operation of the'apparatus at the receiving end of thetransmission line to indicate or register the transmission equivalent of the line at the frequency of the signal being transmitted thereover. This time limitation is a matter of considerable importance, inasmuch as the circuit is out of commercial service while such measurements are being made. It is therefore highly desirable to be able to determine the transmission equivalent of a communication circuit substantially instantaneously. l

This invention resides in a method and means for indicating or recording substantially instantaneously the transmission equivalent of a circuit.

Other objects of this invention will be apparent from the following description when read in connection with the attac-hed drawing, of which Figure 1 shows schematically a form of the invention in which the transmission equivalent is indicated by means of signal lamps; Fig. 1a is a modification of Fig. 1; and Fig. 2 shows a form employing a meter, the said figure also' disclosing means whereby the range of the measuring device may be extended.

In Fig. 1, a source of oscillations l supplies the current to be transmitted over the line L for the determination of the equivalent of this line. This source is connected with the winding 2 of transformer 3 and also with al the line is `connected with an amplifier and rectifier 10, the impedance of which as viewed from the line, being substantially equal to that of the line. The output of the rectifier is connected with the operating windings of a plurality of relays 11 to 15, inclusive. Each lof these relays has a biasing Winding, such as is indicated by 16 of relay 11. By means of the biasing windings, the relays may be made responsive to different Values of line current. The armatures of the relays are connected with a source of potential and a signal lamp, such as 22 and 17, respectively, of relay 11.

The invention as disclosed in Fig. 1 will be clearly understood by a description of the manner in which the circuit, above described, operates. The oscillator 1 is set in operation, and the current limiting device, 4.- is 'varied until the voltage across the networlr7--8-9, as indicated by the meter 6, is of a predetermined value. The voltage across the input of the amplifier 10 will, of course, depend upon the transmission characteristics of the line L. If they are good, the voltage will 'be high, and, if poor, the voltage will be low. This voltage will be amplilied and detected and applied to the operating windings of relays 11 to 15 in parallel. Assuming that the transmission equivalent of the line is equal to 15 TU, (transmission units), the voltage applied to the amplifier 10 will be such that relays 11, 12 and 13 will opcrate, thereby Causing lamps 17, 18 and 19 to be lighted.. If the equivalent were between 15 and 20 TU (but not including'20) the same lamps 17 to 19, inclusive, would be lighted. This would indicate to the operator or other attendant making 'these transmission measurements, that the equivalent of the line was at least as loW as 15 TU. It is, of course, possible to adJust therelays so that smaller units, such as 1 TU or a fraction of a TU, could be measured, if

desired. In like manner, it is possible to arrange the circuits of the armatures of the relays so that ythe lighting of one lamp will extinguish the preceding one, so that, at any instant, only one lampwould be lighted, namely, that closest in proximityto the transmission equivalent of the circuit. Such an arrangement is shown in Fig. 1a which represents the relays and lamp 'circuits of Fig. 1 modified to extinguish all lamps except that one that indicates the transmission equivalent. In Fig. 1, the lamp circuit of relay 11 is normally completed through the contact 23 of rela 12. When the transmitted current is su ciently large to operate relay 12, it opens contact 23, extinguishing lamp 17 and simultaneously closes contact 24, thus lighting lamp 18. As will be seen, each lamp circuit, except that connected with relay 415 is completed through a contact of the succeedin relay.

In tie arrangement shown in Fig. 2, in which the same numbers have been used to represent parts similar to those shown in Fig. 1, the oscillator 1 supplies current for transmission over the line L, the transmission equivalent of which is to be determined. This line is connected with anamplifier 30, the output of which is connected across the potentiometer 3l and also by means of the ranch circuit 32 with an amplifier and rectifier 33. The outut of the amplifier-rectifier 33 is connected With the winding of the relay 34 which is biased by means of the winding 35. This relay controls the connection of the potentiometer 31 with the amplifier and rectifier 36, the output of which is connected with an indicating or recording device 37. The relay 34I also controls the operation of the signal lamp 38, the purpose o which will be clear from subsequent description.

The function of the amplifier and rectifier 33, together with the switching' apparatus connected therewith, is to extend the range of the scale of the device 3 7. Let it be assumed that this scale has a range capable of indicating clearly ten transmission units. For reasons which will be clear from subsequent description, the scale will be marked and subdivided between 10 and 20 TU. When a predeterminedvoltage is impressed across the network 7-8-9, a voltage will be applied to the amplifier 30, whose value depends upon the transmission equivalent of the line L. This volta e, when amplified, will be applied across t e potentiometer 31 and also by means ofthe branch circuit 32, to the amphfier-rectier 33. Assuming that the transmission equivalent is relatively low, for example, of the order of 5 to 10 TU, the voltage applied to the amplifier 30, and also to the Aamplifier-rectifier 33, will be fairly large, that is to say, sufiicient to operate the relay 34. This relay will attract its armatures, and through its left-hand armature, it will connect the in ut of the amplifier-rectifier 36 with the midpoint or a predetermined p oint other than the extremities of the potenf .tlometer 31, which will reduce to a predetermined degree the voltage applied by the amplifier 30 to the ampli er-rectifier 36. This reduction will be sufficient to bring the current in the output of 36 within the limitations of the scale of the indicating device 37 which, as stated, covers the range between 10 and 2O TU. The right-hand armature of relay 34 will close the circuit through the lamp 38 and cause it to light, thus indicating to the operator or other attendant who is making these measurements, that the transmission equivalent indicated by the scale reading of the indieating device is higher by the predetermined amount, 10 TU, than the equivalent actually f is. If, on the other hand, the transmission equivalent of the line L is between 10 and 20 TU, the voltage across the amplifier 30 will be relatively low, so that When amplified and impressed upon the circuit 32 and substantially modified therein, it will not be sufficiently large to operate relay 34. Consequently, the output of amplifier 30 will be applied directly to the input of the amplifier-rectifier 36. The output of this amplifier Will be within the limits of the scale, that is, between 10 and 20 TU, and the reading of the scale of the device 37 will bea direct indication of the transmission equivalent of the line L.

While the invention hasbeen disclosed as embodied in the particular form shown, it is obviously capable of embodiment in other forms, without departing from the spirit and scope of the appended claims.

What is claimed is 1. In a transmission measuring system, the combination with a source of alternating current of fixed magnitude, of a transmission circuit connected with said source capable of attenuating the voltage applied to the circuit by the said source, means connected with the said circuit to indicate substantially instantaneously the equivalent of the circuit in transmission units of a predetermined standard, and means automatically responsive to the received voltage to effectively extend the range of the said indicating device.

2. In a transmission equivalent indicating system the combination with a transmission circuit over which a voltage wave of predetermined magnitude is `transmitted of an indicating circuit connected with the said transmission circuit and having an indicating device, and means automatically responsive to the received voltage to cut down the voltage applied to the said device whenever the transmission equivalent of' the said transmission circuit is greater than a predetermined amount. y

3. In a transmission equivalent indicating system the combination with a transmission circuit over which a voltage wave of predetermined magnitude is transmitted of an indicating circuit connected with the said transmission circuit and having means to amplify to a known degree the received voltage, means to indicate directly the voltage as amplified when the said voltage does not exceed a fixed limit, and means automatically responsive to the received voltage to cut down to a known extent the voltage applied to the said indicating means when the amplified voltage eX- ceeds the limit of direct measurement of the indicating means.

4;. In a transmission equivalent indicating system the combination with a transmission circuit over which 4a voltage wave of predetermined magnitude is transmitted of an indicating circuit connected with the said trans mission circuit and having an amplifier to amplify the received voltage, a rectifier connected with the said amplifier, an indicating device connected with the said rectifier, apotentiometer connected between the said amplifier and rectifier, normally adjusted to apply the full voltage of the amplifier to the rectifier, and means connected with the said amplifier and said potentiometer and automatically responsive to the received voltage to reduce to a known extent the voltage applied to the said rectifier whenever the input voltage of the said amplifier exceeds a predetermined limit.

In testimony whereof, I lhave signed my -name to this specification this 17th day of November, 1926.

, FRED H. BEST. 

